Systems and methods for tri-column code based error reduction

ABSTRACT

Various systems and methods for tri-column code based error reduction are disclosed herein. For example, a digital information system is disclosed that includes channel detector. Such a channel detector receives an encoded data set and provides an output representing the encoded data set. The exemplary system further includes a decoder that receives the first output and is operable to perform three slope parity checks on the received first output. In turn, the decoder provides another output representing the encoded data set.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is related to U.S. patent application Ser. No.11/461,026 entitled “Systems and Methods for Code Dependency Reduction”,by Tan; and U.S. patent application Ser. No. 11/461,283 entitled“Systems and Methods for Code Based Error Reduction”, by Tan. Both ofthe foregoing references are assigned to an entity common hereto, filedon a date common herewith, and incorporated herein by reference in theirentirety for all purposes.

BACKGROUND OF THE INVENTION

The present invention is related to systems and methods for detectingand decoding digital information. More particularly, the presentinvention relates to systems and methods for detecting and correctingerrors associated with an information transfer.

Digital communication systems (e.g., sets of wireless communicationdevices) and digital storage systems (e.g., hard disk drives) providefor transfer of different types of information. For example, in the caseof communication systems, digital information is transferredsubstantially in real time from one communication device to another. Incontrast, digital information transfer involving digital storage systemstypically involves non-real time transfer of digital information thatwas previously stored to a storage device. While there are fundamentaldifferences between the aforementioned information transfer approaches,the general goal of both approaches is to transfer information asaccurately as possible in the presence of impairments such as noise andinter-symbol interference (ISI).

The goal of increasing accuracy of information transfer has fueleddevelopment of progressively more complex information transferapproaches that include increasingly elaborate error correction schemes(ECSs). As an example, a state of the art information transfer approachmay include a substantial number of parity bits built into theinformation being transferred. These parity bits introduce redundancyinto the signal prior to transmission, and are subsequently used todecode the encoded information. FIG. 1 depicts an exemplary state of theart transfer system tailored for a digital storage system. It should benoted that a typical state of the art system tailored for a digitalcommunication system would include the same level of complexity orpossibly greater.

Turning to FIG. 1, a block diagram is provided for a known digitalstorage system 1 that utilizes a parity checking approach for errordetection and correction. Digital storage system 1 includes an encoder 2that encodes information by including parity bits in the information.Encoder 2 is typically a parity based block code encoder. After theoriginal information is encoded, it is provided to recoding channel 3that typically includes various physical and electrical components, suchas a read write head, a read write head armature, a recoding media, apre-amplifier, or other related circuitry or components.

The encoded information is passed from recording channel 3 to a softoutput Viterbi algorithm (SOVA) channel detector 4. SOVA channeldetector 4 processes the received encoded information using a bitdetection algorithm. The output of SOVA channel detector 4 includes acombination of hard decisions and reliability estimates (i.e.,respective estimates as to the reliability of the respective harddecisions). Both the soft and hard outputs of SOVA channel detector 4are provided to a decoder 5 that is responsible for decoding therecovered information bits using the parity bits.

Operation of digital storage system 1 is exemplified where originalinformation (e.g., uk=010110) is to be stored in recording channel 3.The original information is represented by Table 1 below.

TABLE 1 Original Information (uk) 0 1 1 1 0 0

The original information (uk) is provided to encoder 2 that encodes theinformation. Where it is assumed that encoder 2 is a turbo product code(TPC) encoder, a parity bit is added to each row and to each column oftable 1 to produce an even parity code (i.e., each column and each rowcontains an even number of 1's). Thus, the original informationrepresented by a 3×2 table is formed into encoded information (ck) thatis formed in a 4×3 table. The parity laden 4×3 table is represented astable 2 below.

TABLE 2 Original Information Interleaved with Parity (ck) 0 1 1 1 1 0 00 0 1 0 1For simplicity, the example assumes that each column of table 2corresponds to a single parity codeword. It may be, however, that a morecomplex interleaving may be utilized.

In this example the resulting codeword, ck=010111001001, is recorded byrecording channel 3. When retrieved from recording channel 3, a signal(xk) provided from recording channel 3 may be corrupted by noise (nk)resulting in a corrupted signal (yk). The noise (nk) may be, forexample, additive Gaussian noise. SOVA channel detector 4 receives thecorrupted signal (yk) and produces hard decisions and corresponding softreliability estimates. Decoder 5 receives the output of SOVA channeldetector 4 and decodes the output to recover the original informationusing the interleaved parity information.

It has been recognized that various schemes such as the aforementionedscheme are often limited in their ability to detect and correct errors,or they are overly complex resulting in the wasteful use of circuitryand the corresponding waste of power. Hence, for at least theaforementioned reasons, there exists a need in the art for advancedsystems and methods for error reduction.

BRIEF SUMMARY OF THE INVENTION

The present invention is related to systems and methods for detectingand decoding digital information. More particularly, the presentinvention relates to systems and methods for detecting and correctingerrors associated with an information transfer.

Various embodiments of the present invention provide digital informationsystems that include a channel detector. Such a channel detectorreceives an encoded data set and provides an output representing theencoded data set. The systems further include a decoder that receivesthe first output and is operable to perform three slope parity checks onthe received first output. In turn, the decoder provides another outputrepresenting the encoded data set. In some instances of theaforementioned embodiments, the encoded data set is represented ascolumns and rows. In such instances, the slope parity checks operate ona first group of data bits traversing the encoded data set at a firstangle, a second group of data bits traversing the encoded data set at asecond angle, a third group of data bits traversing the encoded data setat a third angle. In some cases the three angles are distinct from oneanother and can be either a zero slope, a greater than zero slope or aless than zero slope. Further, in some instances of the aforementionedembodiments, at least one of the three slopes is programmable.

In some instances of the aforementioned embodiments, each of the slopeparity checks operate on diagonal data bits cutting across the columnsand rows of the encoded data set and including at least one bit fromeach column of the encoded data set. In various cases of theaforementioned embodiments, the channel detector is a soft outputViterbi algorithm channel detector or a MAP. In one or more cases of theaforementioned embodiments, the decoder is a low-density parity checkdecoder.

Other embodiments of the present invention provide methods for errorreduction in a digital information system. Such methods includeproviding an encoded data set that is represented as columns and rows.The encoded data set includes three groups of parity data arranged asthree columns of the encoded data set. The methods further includeproviding a decoding system that includes a channel detector and adecoder. The channel detector receives the encoded data set and providesa channel detector output representative of the encoded data set. Thedecoder receives the channel detector output and performs a three slopeparity checks. One of the slope parity checks uses one group of theparity data, another of the slope parity checks uses another group ofthe parity data, and yet another of the slope parity checks uses theother group of parity data. In some instances of the aforementionedembodiments, the angle of one of the slope parity checks is differentfrom the angle of the other two slope parity checks. Further, in somecases, the angle of at least one of the slope parity checks isprogrammable. In particular cases, the angles of all three of the slopeparity checks are programmable.

In one or more instances of the aforementioned embodiments, a simplisticparity check is implemented where each of the three slope parity checksrelies on parity data from only one of the groups of parity data anddoes not rely on parity data from the other groups of parity data. Thus,the each of the slope parity checks is exclusive of the parity data fromtwo of the three groups of parity data. In other instances of theaforementioned embodiments, a more complex parity check is implementedwhere one of the slope parity checks relies on parity data from allthree groups of parity data, another of the slope parity checks relieson data from two of the three groups of parity data, and the third slopeparity check relies on parity data from only one of the groups of paritydata.

Yet other embodiments of the present invention provide methods for dataencoding. Such methods include receiving an un-encoded data set that isrepresented as an array of columns and rows. Three groups of data bitstraversing the un-encoded data set at respective angles are identified.Parity for one of the groups traversing at one angle is calculated andassembled into a column of parity bits. In addition, parity for anotherof the groups traversing at another angle is calculated and assembledinto another column of parity bits, and parity for the last of thegroups traversing at yet another angle is calculated and assembled intoyet another column of parity bits. In some instances of theaforementioned embodiments, calculating parity for each of the groups isexclusive of parity calculated for any of the other groups. In otherinstances of the aforementioned embodiments, calculating parity for oneor more of the groups includes using parity that was previouslycalculated for one of the other groups.

This summary provides only a general outline of some embodimentsaccording to the present invention. Many other objects, features,advantages and other embodiments of the present invention will becomemore fully apparent from the following detailed description, theappended claims and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

A further understanding of the various embodiments of the presentinvention may be realized by reference to the figures which aredescribed in remaining portions of the specification. In the figures,like reference numerals are used throughout several drawings to refer tosimilar components. In some instances, a sub-label consisting of a lowercase letter is associated with a reference numeral to denote one ofmultiple similar components. When reference is made to a referencenumeral without specification to an existing sub-label, it is intendedto refer to all such multiple similar components.

FIG. 1 is a block diagram of a known digital recording system includinga SOVA channel detector and a decoder implementing an error correctingscheme;

FIGS. 2 a-2 e depict digital recording systems in accordance with one ormore embodiments of the present invention;

FIGS. 3 a-3 b depict two exemplary two stage systems in accordance withone or more embodiments of the present invention are shown;

FIG. 4 shows a hard disk drive system incorporating a combination of achannel detector and a decoder in accordance with various embodiments ofthe present invention;

FIGS. 5 a-5 c together depict a digital recording system in accordancewith various embodiments of the present invention;

FIG. 6 shows a series of decoding stages in accordance with someembodiments of the present invention that may be implemented using thedecoding systems of FIGS. 2 and 5;

FIGS. 7 a-7 c show various encoding methods that may be used inaccordance with one or more embodiments of the present invention;

FIGS. 8 a-8 c show a method for encoding a girth eight code inaccordance with one or more embodiments of the present invention; and

FIG. 9 depicts a software based system 900 in accordance with one ormore embodiments of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is related to systems and methods for detectingand decoding digital information. More particularly, the presentinvention relates to systems and methods for detecting and correctingerrors associated with an information transfer.

Various embodiments of the present invention provide digital informationsystems that include a channel detector. Such a channel detectorreceives an encoded data set and provides an output representing theencoded data set. As used herein, the phrase “encoded data set” is usedin its broadest sense to mean any set of data which includes some levelof encoding. Thus, for example, an encoded data set may include, but isnot limited to a set of data that is augmented to include one or moreparity bits. The systems further include a decoder that receives thefirst output and is operable to perform three slope parity checks on thereceived first output. In turn, the decoder provides another outputrepresenting the encoded data set. As used herein, the phrase “slopeparity check” is used in its broadest sense to mean a check of paritybased on a group of data bits represented as a straight line across anarray of data bits whether the line is horizontal or diagonal.

In some instances of the aforementioned embodiments, the encoded dataset is represented as columns and rows. In such instances, the slopeparity checks operate on a first group of data bits traversing theencoded data set at a first angle, a second group of data bitstraversing the encoded data set at a second angle, a third group of databits traversing the encoded data set at a third angle. In some cases thethree angles are distinct from one another and can be either a zeroslope, a greater than zero slope or a less than zero slope. Further, insome instances of the aforementioned embodiments, at least one of thethree slopes is programmable. It should be noted that the terms“columns” and “rows” are used in their broadest sense to mean straightlines of data intersecting at ninety degree angles. Thus, for example,an encoded data set may be represented to include horizontal columns andvertical rows, or horizontal rows and vertical columns.

Turning to FIG. 2 a, a digital recording system 200 in accordance withone or more embodiments of the present invention is depicted. Digitalrecording system 200 includes an encoder 220 capable of receiving anoriginal data set 210 and encoding original data set 210 as a twodimensional data set 222 arranged in a number of columns (Nc) and anumber of rows (Nr). It should be noted that two dimensional data set222 may be rotated ninety degrees such that the rows become vertical andthe columns become horizontal. Encoder 220 performs a low density paritycheck encoding using a three-dimensional single parity encodingalgorithm. The first dimension includes a group of parity data arrangedas a row 224 of encoded data set 222. In one embodiment of the presentinvention, row 224 is formed by adding one even parity bit for eachcolumn of encoded data set 222. Thus, as an example, where the firstcolumn of encoded data set includes an odd number of ‘1s’, the first bitof row 224 will be a ‘1’. Alternatively, where the first column ofencoded data set 222 includes an even number of ‘1s’, the first bit ofrow 224 will be a ‘0’. Based on the disclosure provided herein, one ofordinary skill in the art will recognize a variety of other encodingapproaches that may be implemented via row 224. For example, row 224 maybe utilized to implement odd parity.

The second dimension includes a group of parity data arranged as acolumn 226 of encoded data 222, and the third dimension includes a groupof parity data arranged as a column 228 of encoded data 222. In oneembodiment of the present invention, column 226 and column 228 areformed by adding one even parity bit at each bit location of therespective column with the even parity bit being associated with eithera pseudo-random assortment of data bits from encoded data set 222, or asloping assortment of data bits from encoded data set 222. In oneparticular case, each even parity bit of column 226 and/or column 228 isassociated with a group of data bits formed by applying a pseudo-randomselection algorithm that selects one bit from each column of encodeddata set 222. Thus, for example, where there are ten columns included inencoded data set 222, one bit from each column or ten bits are firstpseudo-randomly selected. Then, where the ten bits includes an evennumber of ‘1s’, a ‘0’ is written to the associated bit location ofcolumn 226 or column 228. Alternatively, where the ten bits includes anodd number of ‘1s’, a ‘1’ is written to the associated bit location ofcolumn 226 or column 228.

In another particular case, each even parity bit of column 226 and/orcolumn 228 is associated with a diagonal group of data bits from encodeddata set 222. The diagonal proceeds at a given slope through encodeddata set 222. For example, where the slope is zero, the diagonal groupof data bits comprises a single row of data bits concluding with anassociated parity bit in column 228 that corresponds to the row. Asanother example, where the slope is greater than zero, the diagonalgroup of data bits comprises bits from different rows moving in agenerally straight line across encoded data set 222 and concluding withan associated parity bit in column 228 that corresponds to the slope ofthe diagonal. Where the bits in the diagonal include an even number of‘1s’, a ‘0’ is added at the prescribed location of column 228.Alternatively, where the bits in the diagonal include an odd number of‘1s’, a ‘1’ is added at the prescribed location of column 228. Based onthe disclosure provided herein, one of ordinary skill in the art willrecognize a variety of other encoding approaches that may be implementedvia column 226 and column 228. For example, column 226 and column 228may be utilized to implement odd parity.

It should be noted that in some embodiments of the present invention,the second and third dimensions are encoded and decoded usinginterleavers, and the first dimension is encoded and decoded without theuse of interleavers. More particularly, in such cases, the parity bitsincluded in column 226 and column 228 are not parities for a single rowof data bits (except in the condition where the slope is equal to zeroin which case the third dimension includes parities for a particularrow). In some embodiments of the present invention, regardless of thesingle parity code of the first dimension, the single parity codes forthe second and third dimensions compose a mostly regular low-densityparity check code of column weight two (i.e., j=2), except for theparticular cases where the parity bits exhibit a column weight of one(i.e., j=1). For this reason, such codes are generally referred toherein as a low-density single parity check code. It should be notedthat the encoding of the second and third dimensions of the low-densityparity check code may be extended to any regular or irregularlow-density parity check codes of column weight two.

Once the encoding process is complete, encoded data set 222 of size(Nr+1) rows and (Nc+2) columns are written to a disk by recordingchannel 240 on a column by column basis. At this juncture it should benoted that one of ordinary skill in the art upon reading this disclosurewill recognize that writing the data to disk may be done on anotherbasis such as, for example, a row by row basis if such was desired andthe appropriate accommodations were made. Further, based on reading thisdisclosure, one of ordinary skill in the art will recognize that theprocess of writing to disk may be replaced by another transmissionactivity depending upon the system in which the embodiments of thepresent invention are being deployed. Thus, for example, where theparticular embodiment of the present invention is being deployed in awireless communication system, recording channel 240 may be replaced bya transmitter and a receiver. In such cases, rather than the action ofwriting to disk, the action may include transmitting encoded data set222. The encoded data set would then be received by a receiver, ratherthan accessed from a disk. Again, based on the disclosure providedherein, one of ordinary skill in the art will recognize a variety ofother applications in which embodiments of the present invention may bedeployed, and actions applied to encoded data set 222 based on theparticular application.

At some point the written encoded data 222 is accessed from the disk byrecording channel 240 and provided to a channel detector 260. Channeldetector 260 includes a simple column parity calculator 262. Simplecolumn parity checker 262 operates on the parity information containedin row 224 to perform an error detection/error correction function. Asthe parity for row 224 is calculated on a column by column basis, nointerleaver is necessary to perform the error detection/error correctionfunction. Channel detector 260 provides an output 264 incorporating theresults of simple column parity 262 to a decoder 280. In someembodiments of the present invention, output 264 includes a soft output(i.e., reliability information). In some cases, where the soft outputhas not exceeded a predetermined reliability threshold, it is fed backto channel detector 260 as an output 288 from decoder 280. In particularcases, the soft output is increased by application of errordetection/error correction implemented by decoder 280 as discussedbelow. In other cases, the soft output is simply fed back to channeldetector 260 without modification where it is used as a prioriinformation for further refinement in determining an increasedreliability factor. It should be noted that such feedback is optionaland in some cases may be replaced by a series of decoding stages as morefully discussed below in relation to FIG. 6.

Decoder 280 includes a pseudo-random parity check 282 and/or a slopeparity check 284. In one particular case, pseudo-random parity check 282operates on the parity information contained in column 226, and slopeparity check 284 operates on the parity information contained in column228. In another particular embodiment of the present invention,pseudo-random parity check 282 operates on the parity informationcontained in both column 226 and column 228. In yet another particularembodiment of the present invention, slope parity check 226 operates onthe parity information contained in both column 226 and column 228. Aspseudo-random parity check 282 and slope parity check 284 do not operateon columns, de-interleavers are included in decoder 280 to assemble theproper bits associated with each respective parity bit in column 226 andcolumn 228. In particular, each of pseudo-random parity check 282 andslope parity check 284 individually performs a single parity errordetection/error correction algorithm and the output of each of theaforementioned parity checks is summed or otherwise combined to providea decoder output 290. In some cases, decoder output 290 includes a softoutput (i.e., reliability information). In some cases, where the softoutput has not exceeded a predetermined reliability threshold, it is fedback to decoder 280 as an output 286 from decoder 280. Thus, thereliability information may be iteratively used to detect and/or correctany errors in encoded data set 222. Again, it should be noted that suchfeedback is optional and in some cases may be replaced by a series ofdecoding stages as more fully discussed below in relation to FIG. 6. Asone of various advantages, digital recording system 200 provides asignificant gain in signal to noise ratio when compared with otherencoding/decoding architectures, yet requires only a moderate increasein design complexity when compared with the same architectures.

Turning to FIG. 2 b, a digital recording system 201 in accordance withother embodiments of the present invention is depicted. Digitalrecording system 201 includes encoder 220, encoded data set 222 andrecording channel 240 as described in relation to digital recordingsystem 200 above. In digital recording system 201, column parity isimplement in relation to a soft output Viterbi algorithm (SOVA) channeldetector 261. As only a single bit parity scheme is implemented, channeldetector 261 is referred to as a SOVAsp channel detector. Thepseudo-random parity and/or slope parity checks are implemented as partof a low-density parity check (LDPC) decoder 281. As both pseudo-randomparity check and slope parity check are each single bit parity schemes,decoder 281 is referred to as an SP-based, LDPC decoder.

In operation, SOVAsp channel detector 261 performs a column parity checkusing parity data from row 224. Based on this column parity check, anoutput 265 is provided to SP-based, LDPC decoder 281. Output 265includes reliability information regarding bits decoded from encodeddata set 222. In some cases, where the reliability information has notexceeded a predetermined reliability threshold, it is fed back tochannel detector 261 as an output 289 from SP-based, LDPC decoder 281.In particular cases, the reliability information is increased byapplication of error detection/error correction implemented by SP-based,LDPC decoder 281 as discussed below. In other cases, the reliabilityinformation is simply fed back to SOVAsp channel detector 261 withoutmodification where it is used as a priori information for furtherrefinement in determining an increased reliability factor. As before, itshould be noted that such feedback is optional and in some cases may bereplaced by a series of decoding stages as more fully discussed below inrelation to FIG. 6.

SP-based, LDPC decoder 281 performs a pseudo-random parity check and/ora slope parity check. The pseudo-random parity check may operate on theparity information contained in one or more of column 226 and column228, and the slope parity check may operate on the parity informationcontained in one or more of column 226 and column 228. Again, as thepseudo-random parity check and the slope parity check do not operate oncolumns, de-interleavers are included in SP-based, LDPC decoder 281 toassemble the proper bits associated with each respective parity bit incolumn 226 and column 228. In particular, each of the pseudo-randomparity check and the slope parity check individually performs a singleparity error detection/error correction algorithm and the output of eachof the aforementioned parity checks is summed or otherwise combined toprovide a decoder output 291. In some cases, decoder output 291 includesreliability information. In some cases, where the reliabilityinformation has not exceeded a predetermined reliability threshold, itis fed back to SP-based LDPC decoder 281 as an output 287 from SP-based,LDPC decoder 281. Thus, the reliability information may be iterativelyused to detect and/or correct any errors in encoded data set 222. Again,it should be noted that such feedback is optional and in some cases maybe replaced by a series of decoding stages as more fully discussed belowin relation to FIG. 6. As one of various advantages of the embodimentsof the present invention, digital recording system 200 provides asignificant gain in signal to noise ratio when compared with otherencoding/decoding architectures, yet requires only a moderate increasein design complexity when compared with the same architectures.

Turning to FIG. 2 c, an exemplary encoded data set 222 including elevencolumns (C1-C11) and nine rows (R1-R9) of encoded data is depicted. Inaddition, row 224 of thirteen column parity bits, column 226 of tenpseudo-random parity bits, and column 228 of ten slope parity bits areincluded. As previously discussed, row 224 includes individual paritybits associated with respective columns of encoded data set 222. Forexample, row 224 includes a parity bit 237 used to provide apredetermined parity to a column 233.

Column 226 includes individual parity bits associated with groups ofpseudo-randomly selected data bits from encoded data 222. In some cases,this includes one bit from each column of encoded data 222. As just oneexample, a parity bit 225 in column 226 is associated with a group ofdata bits including a data bit 211 from column C1, a data bit 212 fromcolumn C2, a data bit 213 from column C3, a data bit 214 from column C4,a data bit 215 from column C5, a data bit 216 from column C6, a data bit217 from column C7, a data bit 218 from column C8, a data bit 219 fromcolumn C9, and a data bit 221 from column C10, and a data bit 223 fromcolumn C11.

Column 228 includes individual parity bits associated with a groups ofdata bits traversing encoded data 222 at a given angle 239. In somecases, this includes one bit from each column of encoded data 222. Asjust one example, a parity bit 227 in column 228 is associated with agroup of data bits including a data bit 297 from column C1, a data bit251 from column C2, a data bit 252 from column C3, a data bit 253 fromcolumn C4, a data bit 254 from column C5, a data bit 255 from column C6,a data bit 217 from column C7, a data bit 257 from column C8, a data bit258 from column C9, and a data bit 259 from column C10, a data bit 295from column C11, and a data bit 296 from pseudo-random parity column226. Other parity bits within column 228 are associated with similardiagonal groups of parity bits traversing encoded data set 222 at thesame angle 239 such that all bits in encoded data set 222 are used inthe parity checking scheme. As a simple example, where angle 239 iszero, each row (R1-R9 row 224) are associated with a respective paritybits in column 228. In one particular embodiment of the presentinvention, angle 239 is programmable such that different groupings ofdata associated with a given parity bit can be achieved. It should benoted that diagonal, horizontal, and anti-diagonal slopes may be definedin any given data set. Further, in some cases, the parity bits includedwithin the diagonal are not included in any slope parity check. Thus,using the example of FIG. 2 c, parity bit 296 may not be associated withdiagonal parity data 230 and parity bit 227. In some cases, to make thecode associated with column 228 more random, the diagonals are firstformed, and subsequently a column random interleaver may be applied toincrease the randomness of the codes.

It should be noted that the number of columns and rows depicted in FIG.2 c is merely exemplary. Based on the disclosure provided herein, one ofordinary skill in the art will appreciate a variety of other column androw dimensions that may be used to achieve desired design constraints.For example, the data may be arranged in a 4×4 array plus two addedparity columns and an added parity row. In some embodiments of thepresent invention, the parity check matrix is not maintained inhardware, but rather can be calculated from the included interleavers.Further, the code length, rate, column weight of the parity checkmatrix, and/or the slope can be programmable. Such embodiments provide agreat deal of programmability that can be tailored to meet a particularcircumstance.

Turning to FIG. 2 d, exemplary encoded data set 222 including elevencolumns (C1-C11) and nine rows (R1-R9) of encoded data is againdepicted. In addition, row 224 of thirteen column parity bits, column226 of ten slope parity bits, and column 228 of ten slope parity bitsare included. As previously discussed, row 224 includes individualparity bits associated with respective columns of encoded data set 222.For example, row 224 includes a parity bit 237 used to provide apredetermined parity to a column 233.

Column 226 includes individual parity bits associated with group 230 ofdata bits traversing encoded data 222 at angle 239. Other parity bitswithin column 226 are associated with similar diagonal groups of paritybits traversing encoded data set 222 at the same angle 239 such that allbits in encoded data set 222 are used in the parity checking scheme.Column 228 includes individual parity bits associated with group 241 ofdata bits traversing encoded data 222 at an angle 299. As just oneexample, a parity bit 266 in column 228 is associated with a group ofdata bits including a data bit 242 from column C1, a data bit 243 fromcolumn C2, a data bit 244 from column C3, a data bit 245 from column C4,a data bit 246 from column C5, a data bit 247 from column C6, a data bit248 from column C7, a data bit 249 from column C8, a data bit 298 fromcolumn C9, and a data bit 263 from column C10, and a data bit 223 fromcolumn C11. Other parity bits within column 228 are associated withsimilar diagonal groups of parity bits traversing encoded data set 222at the same angle 299 such that all bits in encoded data set 222 areused in the parity checking scheme.

Again, it should be noted that the number of columns and rows depictedin FIG. 2 d is merely exemplary. Based on the disclosure providedherein, one of ordinary skill in the art will appreciate a variety ofother column and row dimensions that may be used to achieve desireddesign constraints. For example, the data may be arranged in a 4×4 arrayplus two added parity columns and an added parity row. In someembodiments of the parity check matrix is not maintained in hardware,but rather can be calculated from the included interleavers. Further,the code length, rate, column weight of the parity check matrix, and/orthe slope can be programmable. Such embodiments provide a great deal ofprogrammability that can be tailored to meet a particular circumstance.

Turning to FIG. 2 e, exemplary encoded data set 222 including elevencolumns (C1-C11) and nine rows (R1-R9) of encoded data is againdepicted. In addition, row 224 of thirteen column parity bits, column226 of ten slope parity bits, and column 228 of ten slope parity bitsare included. As previously discussed, row 224 includes individualparity bits associated with respective columns of encoded data set 222.For example, row 224 includes a parity bit 237 used to provide apredetermined parity to a column 233.

Column 226 includes individual parity bits associated with groups ofpseudo-randomly selected data bits from encoded data 222. As just oneexample, parity bit 225 in column 226 is associated with a group of databits including data bit 211 from column C1, data bit 212 from column C2,data bit 213 from column C3, data bit 214 from column C4, data bit 215from column C5, data bit 216 from column C6, data bit 217 from columnC7, data bit 218 from column C8, data bit 219 from column C9, and databit 221 from column C10, and data bit 223 from column C11. Column 228also includes individual parity bits associated with groups ofpseudo-randomly selected data bits from encoded data 222. As just oneexample, parity bit 207 in column 228 is associated with a group of databits including a data bit 267 from column C1, data bit 268 from columnC2, data bit 269 from column C3, data bit 208 from column C4, data bit227 from column C5, data bit 229 from column C6, data bit 209 fromcolumn C7, data bit 203 from column C8, data bit 204 from column C9, anddata bit 205 from column C10, and data bit 206 from column C11.

Again, it should be noted that the number of columns and rows depictedin FIG. 2 d is merely exemplary. Based on the disclosure providedherein, one of ordinary skill in the art will appreciate a variety ofother column and row dimensions that may be used to achieve desireddesign constraints. For example, the data may be arranged in a 4×4 arrayplus two added parity columns and an added parity row. In someembodiments of the parity check matrix is not maintained in hardware,but rather can be calculated from the included interleavers. Further,the code length, rate, column weight of the parity check matrix, and/orthe slope can be programmable. Such embodiments provide a great deal ofprogrammability that can be tailored to meet a particular circumstance.

In some embodiments of the present invention, the iterative paritychecking is replaced or augmented by forming a series of channeldetectors and decoders. As one particular example, decoder output 290may be provided to another channel detector that in turn feeds anotherdecoder. This can be repeated for as many serial stages as desired.Turning to FIG. 3, two exemplary two stage systems 400, 401 aredepicted. In system 400, a SOVAsp 410 and a delay element 440 receivesan encoded data set. SOVAsp performs a column parity check and providesan output to, for example, a TPC decoder 420 that performs both thevarious TPC parity checks including re-decoding of the column paritybits decoded by SOVAsp 410. TPC decoder 420 then provides the refinederror calculation to a hard output Viterbi channel detector 430 whichreceives the delayed original encoded data and again performs a refinedcolumn parity check. Based on the disclosure provided herein, one ofordinary skill in the art will recognize a myriad of stages includingadditional SOVA channel detectors, decoders and hard output channeldetectors that may be employed in accordance with one or moreembodiments of the present invention. Turning to FIG. 3 b, system 401includes an LDPC decoder 421 in place of the TPC decoder of system 400to perform substantially the same function.

Turning to FIG. 4, an exemplary embodiment of the present invention isdeployed in relation to a hard disk drive system 300. Hard disk drivesystem 300 includes a disk platter 310 that provides a magnetic storagemedium. Hard disk drive system 300 includes a decoder 380 that providesone or both of a pseudo-random parity check 382 and a slope parity check384, and a channel detector 360 that provide a column parity check 362.An output 364 from channel detector 360 is provided to decoder 380, andan output 390 from decoder 380 is provided to an interface (not shown)of hard disk drive system 300. In addition, an output 386 of decoder 380is fed back to itself while an output 388 of decoder 380 is fed back tochannel detector 360. In addition, hard disk drive system 300 includes ahard disk controller 330, a motor controller 340, a preamp 320, aspindle motor 350, and a read/write head assembly 318.

The data on disk platter 310 consists of groups of magnetic signals thatmay be detected by read/write head assembly 318 when the assembly isproperly positioned over disk platter 310. In a typical read operation,read/write head assembly 318 is accurately positioned by motorcontroller 340 over a desired data track on disk platter 310. Motorcontroller 340 both positions read/write head assembly 318 in relationto disk platter 310 and drives spindle motor 350 by moving read/writehead assembly to the proper data track on disk platter 310 under thedirection of hard disk controller 330. Spindle motor 350 spins diskplatter 310 at a determined spin rate (RPMs).

Once read/write head assembly 310 is positioned adjacent the proper datatrack, magnetic signals representing data on disk platter 310 are sensedby read/write head assembly 318 as disk platter 310 is rotated byspindle motor 350. The sensed magnetic signals are provided as acontinuous, minute analog signal representative of the magnetic data ondisk platter 310. This minute analog signal is transferred fromread/write head assembly 318 to channel detector 360 via preamp 320.Preamp 320 is operable to amplify the minute analog signals accessedfrom disk platter 310. An analog to digital converter (not shown)digitizes the received analog signal and the combination of decoder 380and channel detector 360 work on the digitized signal to recreate thedigital data originally written to disk platter 310. Channel detector360 and decoder 380 operate in accordance with one or more of theembodiments discussed above in relation to channel detectors 260, 261and decoders 280, 281. The digitized data is provided via an interface(not shown) to a host computer or device governing operation of harddisk drive system 300.

Turning now to FIG. 5 a, a digital recording system 500 in accordancewith various embodiments of the present invention is depicted. Digitalrecording system 500 includes an encoder 520 capable of receiving anoriginal data set 510 and encoding original data set 510 as a twodimensional data set 522 arranged in a number of columns (Nc) and anumber of rows (Nr). It should be noted that two dimensional data set522 may be rotated ninety degrees such that the rows become vertical andthe columns become horizontal. Encoder 520 performs a low density paritycheck encoding using a three-dimensional single parity encodingalgorithm. The first dimension includes a group of parity data arrangedas a column 524 of encoded data set 522, the second dimension includes agroup of parity data arranged as a column 526 of encoded data 522, andthe third dimension includes a group of parity data arranged as a column528 of encoded data 522.

In some cases of the aforementioned embodiment of the present invention,all three dimensions utilize a slope parity check using a differentslope angle for each of the columns 524, 526, 528 of parity data. Inother cases of the aforementioned embodiment of the present invention,all three dimensions utilize a pseudo-random parity check for each ofthe columns 524, 526, 528 of parity data. In yet other cases of theaforementioned embodiment of the present invention, the three dimensionsare some combination of slope parity check(s) and pseudo-random paritycheck(s). In some cases of the aforementioned embodiment even parity isused, while in other cases odd parity is used.

Once the encoding process is complete, encoded data set 522 of size (Nr)rows and (Nc+3) columns are written to a disk by recording channel 540on a column by column basis. At this juncture it should be noted thatone of ordinary skill in the art upon reading this disclosure willrecognize that writing the data to disk may be done on another basissuch as, for example, a row by row basis if such was desired and theappropriate accommodations were made. Further, based on reading thisdisclosure, one of ordinary skill in the art will recognize that theprocess of writing to disk may be replaced by another transmissionactivity depending upon the system in which the embodiments of thepresent invention are being deployed. Thus, for example, where theparticular embodiment of the present invention is being deployed in awireless communication system, recording channel 540 may be replaced bya transmitter and a receiver. In such cases, rather than the action ofwriting to disk, the action may include transmitting encoded data set522. The encoded data set would then be received by a receiver, ratherthan accessed from a disk. Again, based on the disclosure providedherein, one of ordinary skill in the art will recognize a variety ofother applications in which embodiments of the present invention may bedeployed, and actions applied to encoded data set 522 based on theparticular application.

At some point the written encoded data 522 is accessed from the disk byrecording channel 540 and provided to a channel detector 560. Channeldetector 560 may be any soft input/soft output channel detector such as,for example, a SOVA (Soft Output Viterbi Algorithm Decoder) or MAP(Maximum A Posteriori Probability) channel detector as are known in theart. Channel detector 560 provides an output 564 to a decoder 580. Insome cases, decoder 580 is a simple parity based LDPC decoder. In someembodiments of the present invention, output 264 includes a soft output(i.e., reliability information). In some cases, where the soft outputhas not exceeded a predetermined reliability threshold, it is fed backto channel detector 560 as an output 588 from decoder 580. In particularcases, the soft output is increased by application of errordetection/error correction implemented by decoder 580 as discussedbelow. In other cases, the soft output is simply fed back to channeldetector 560 without modification where it is used it is used as apriori information for further refinement in determining an increasedreliability factor. It should be noted that such feedback is optionaland in some cases may be replaced by a series of decoding stages as morefully discussed below in relation to FIG. 6.

Decoder 580 includes a pseudo-random parity check 582 and/or a slopeparity check 584 depending upon how data bits 510 are encoded. Forexample, in one particular case, slope parity check 284 operates on theparity information contained in columns 524, 526, 528. In such cases,pseudo-random parity check 582 may not be included in decoder 580.Decoder 580 provides an output 590 that in some cases includes a softoutput (i.e., reliability information). In some cases, where the softoutput has not exceeded a predetermined reliability threshold, it is fedback to decoder 580 as an output 586 from decoder 580. Thus, thereliability information may be iteratively used to detect and/or correctany errors in encoded data set 522. It should be noted that suchfeedback is optional and in some cases may be replaced by a series ofdecoding stages as more fully discussed below in relation to FIG. 6. Asone of various advantages, digital recording system 500 provides asignificant gain in signal to noise ratio when compared with otherencoding/decoding architectures, yet requires only a moderate increasein design complexity when compared with the same architectures. Itshould be noted that digital recording system 500 can be used inrelation to hard disk drive system 300. In particular, channel detector560 may be used in place of channel detector 360, and SP-based LDPCdecoder 580 may be used in place of decoder 380.

FIGS. 5 b and 5 c show two exemplary slope encodings of an exemplarydata set 522. As shown, exemplary data set 522 includes eleven columns(C1-C11) and nine rows (R1-R9) of encoded data. In addition, column 524of nine slope parity bits, column 526 of nine slope parity bits, andcolumn 528 of nine slope parity bits are included. Each of the bits incolumns 524, 526, 528 is associated with a respective group 570, 575,530 of data bits traversing encoded data 522 at a given angle. In somecases, this includes one bit from each column of encoded data 522. Asjust one example, a parity bit 513 in column 524 is associated with agroup of data bits including a data bit 501 from column C1, a data bit502 from column C2, a data bit 503 from column C3, a data bit 504 fromcolumn C4, a data bit 505 from column C5, a data bit 506 from column C6,a data bit 507 from column C7, a data bit 508 from column C8, a data bit509 from column C9, a data bit 511 from column C10, a data bit 512 fromcolumn C11. Other parity bits within column 524 are associated withsimilar diagonal groups of parity bits traversing encoded data set 522at an angle 589 such that all bits in encoded data set 522 are used inthe parity checking scheme. As a simple example, where angle 589 iszero, each row (R1-R9) are associated with a respective parity bits incolumn 524. In one particular embodiment of the present invention, angle589 is programmable such that different groupings of data associatedwith a given parity bit can be achieved. It should be noted thatdiagonal, horizontal, and anti-diagonal slopes may be defined in anygiven data set. In the case depicted in FIG. 5 b, the parity bitsincluded within the diagonal are not included in any other slope paritycheck (i.e., there is one parity bit included in each group 570, 575,530).

Continuing the example, a parity bit 556 in column 526 is associatedwith a group of data bits including a data bit 544 from column C1, adata bit 545 from column C2, a data bit 546 from column C3, a data bit547 from column C4, a data bit 548 from column C5, a data bit 549 fromcolumn C6, a data bit 551 from column C7, a data bit 552 from column C8,a data bit 553 from column C9, a data bit 554 from column C10, and adata bit 555 from column C11. The preceding group traverses encoded dataset 522 at an angle 587. Other parity bits within column 526 areassociated with similar diagonal groups of parity bits traversingencoded data set 522 at angle 587 such that all bits in encoded data set522 are used in the parity checking scheme. A parity bit 543 in column528 is associated with a group of data bits including a data bit 531from column C1, a data bit 533 from column C2, a data bit 534 fromcolumn C3, a data bit 535 from column C4, a data bit 536 from column C5,a data bit 537 from column C6, a data bit 538 from column C7, a data bit539 from column C8, a data bit 509 from column C9, a data bit 541 fromcolumn C10, and a data bit 542 from column C11. The preceding grouptraverses encoded data set 522 at an angle 585. Other parity bits withincolumn 528 are associated with similar diagonal groups of parity bitstraversing encoded data set 522 at angle 585 such that all bits inencoded data set 522 are used in the parity checking scheme.

Turning to FIG. 5 c, a similar set of diagonal groups of parity bits isdepicted. In this case, however, multiple parity bits are included inthe diagonal groups. In particular, a group 592 includes all of the databits included with the aforementioned group 530. In addition, group 592includes a parity bit 595 from column 524 and a parity bit 596 fromcolumn 526. Parity bit 543 operates as a simple parity bit for group 592with parity bit 595 and parity bit 596 being treated the same as theother data bits for the purposes of the parity calculation for group592. A group 591 includes all of the data bits included with theaforementioned group 575. In addition, group 591 includes a parity bit597 from column 524. Parity bit 556 operates as a simple parity bit forgroup 591 with parity bit 597 being treated the same as the other databits for the purposes of the parity calculation for group 591. Based onthe disclosure provided herein, one of ordinary skill in the art willrecognize that encoding the data set discussed in FIG. 5 c is somewhatmore complex that encoding that of FIG. 5 b. Further, one of ordinaryskill in the art will recognize that an iterative encoding may beperformed where each of the diagonal groups may include three paritybits. In such cases, only the parity bit in the column associated withthe group acts as a simple parity bit with the other parity bits beingtreated similar to the data bits. Yet further, based on the disclosureprovided herein, one of ordinary skill in the art will recognize thatcolumns 524, 526, 528 may be associated with groups of pseudo-randombits, or a combination of diagonal groups and pseudo-random groups.

It should be noted that the number of columns and rows depicted in FIGS.5 b and 5 c is merely exemplary. Based on the disclosure providedherein, one of ordinary skill in the art will appreciate a variety ofother column and row dimensions that may be used to achieve desireddesign constraints. For example, the data may be arranged in a 4×4 arrayplus two added parity columns and an added parity row. In someembodiments of the parity check matrix is not maintained in hardware,but rather can be calculated from the included interleavers. Further,the code length, rate, column weight of the parity check matrix, and/orthe slope can be programmable. Such embodiments provide a great deal ofprogrammability that can be tailored to meet a particular circumstance.

Turning to FIG. 6, a system 600 in accordance with one or moreembodiments of the present invention is disclosed. System 600 includes aseries of four stages with the first stage including a channel detector625, an LDPC decoder 645, and a delay 605. The second stage includes achannel detector 630, a delay 660, a summer 662, an LDPC decoder 650,and a delay 610. The third stage includes a channel detector 635, adelay 665, a summer 667, an LDPC decoder 655, and a delay 615. Thefourth stage includes a hard output Viterbi decoder 640. System 600shows a general iterative system into which decoder 280 and channeldetector 260 may be deployed in place of the respective channeldetectors and LDPC decoders of the various stages. Alternatively,decoder 281 and channel detector 261 may be deployed in place of therespective channel detectors and LDPC decoders of the various stages. Asyet another alternative, decoder 580 and channel detector 560 may bedeployed in place of the respective channel detectors and LDPC decodersof the various stages. Thus, such an iterative approach may be appliedin relation to a number of embodiments of the present invention.

Turning to FIGS. 7 a-7 c, flow diagrams 740, 750 depict exemplaryembodiments for encoding data sets in accordance with one or moreembodiments of the present invention. In particular, flow diagram 740shows a method for encoding data sets such as those shown in FIGS. 2 cand 2 d. It is determined whether column 226 and column 228 are to beencoded as slope parity or pseudo-random parity (block 741). Where slopeparity is to be used for both columns (block 741), a column paritymodule 710 is called to calculate column parity for each column of dataset 222. In addition, two instances of a slope parity module 730 arecalled in parallel with one tasked with calculating slope parityassociated with column 226 and the other tasked with calculating slopeparity associated with column 228. Alternatively, where pseudo-randomparity is to be used for both columns (block 741), column parity module710 is called to calculate column parity for each column of data set222. In addition, two instances of a pseudo-random parity module 720 arecalled in parallel with one tasked with calculating pseudo-random parityassociated with column 226 and the other tasked with calculatingpseudo-random parity associated with column 228. Each of column paritymodule 710, pseudo-random parity module 720, and slope parity module 730are discussed in more detail below in relation to FIG. 7 c below. Oncethe modules have completed, the encoding process is completed (block742). Based on the disclosure provided herein, one of ordinary skill inthe art will appreciate that flow diagram 740 can be modified to allowfor calculating pseudo-random parity for one of the columns and slopeparity for the other column.

Flow diagram 750 shows a method for encoding data sets such as thoseshown in FIGS. 5 b and 5 c. It is determined whether columns 524, 526,528 are to be encoded as dependent or non-dependent parity (block 751).As used in this example, non-dependent parity implies a single paritybit included in each of groups 530, 570, 575 as shown in FIG. 5 b. Incontrast, dependent parity implies a single parity bit for one group,two parity bits for the next group (one of the parity bits being treatedsimilar to the data bits), and three parity bits for the last group (twoof the parity bits being treated similar to the data bits). Wherenon-dependent parity is to be used (block 751), three instances of slopeparity module 730 are called in parallel with one tasked withcalculating slope parity associated with column 524, another tasked withcalculating slope parity associated with column 526, and the othertasked with calculating slope parity associated with column 528. Oncethe modules complete, the encoding is done (block 752). Of note, parityfor each of the columns can be calculated in parallel making encodingrelatively fast.

Alternatively, where dependent parity is to be used (block 751), aninstance of slope parity module 730 is called to calculate slope parityassociated with column 524. Then, once column 524 is complete, aninstance of slope parity module 730 is called to calculate slope parityassociated with column 526 that includes the parity data of column 524(similar to that discussed in relation to FIG. 5 c above). Then, oncecolumn 526 is complete, an instance of slope parity module 730 is calledto calculate slope parity associated with column 528 that includes theparity data of column 524 and column 526 (similar to that discussed inrelation to FIG. 5 c above). Once the modules complete, the encoding isdone (block 752). Such encoding takes additional time when compared tothe aforementioned parallel example, but may result in a more robustcode.

Turning to FIG. 7 c, flow diagrams representing column parity module710, pseudo-random parity module 720 and slope parity module 730 areshown. Following the flow diagram associated with column parity module710, a pointer is set to the first column of a data set (block 711), andthe parity for the column is calculated by accounting for each data bitwithin the column (block 712). The calculated parity is stored to aparity row (block 713). It is determined whether the last paritycalculated was for the last column of the data set (block 714). If it isnot the last column (block 714), the column pointer is incremented(block 715) and the parity calculation and storage is repeated for thenext column (blocks 712, 713). This process continues until parity forall columns is calculated and stored at which time the module completesand returns (block 716).

Following the flow diagram associated with pseudo-random parity module720, groups of pseudo random bits associated with each parity bit arecalculated (block 721) and a pointer is set to the first group (block722). Parity for the group is by accounting for each data bit within thegroup (block 723). The calculated parity is stored to a parity column(block 724). It is determined whether the current parity calculation wasfor the last group of the data set (block 725). If it is not the lastgroup (block 725), the group pointer is incremented (block 727) and theparity calculation and storage is repeated for the next group (blocks723, 724). This process continues until parity for all groups iscalculated and stored at which time the module completes and returns(block 726).

Following the flow diagram associated with slope parity module 730,diagonal groups of bits associated with each parity bit are calculated(block 731) and a pointer is set to the first group (block 732). Parityfor the group is by accounting for each data bit within the group (block733). The calculated parity is stored to a parity column (block 734). Itis determined whether the last parity calculated was for the last groupof the data set (block 735). If it is not the last group (block 735),the group pointer is incremented (block 737) and the parity calculationand storage is repeated for the next group (blocks 733, 734). Thisprocess continues until parity for all groups is calculated and storedat which time the module completes and returns (block 736).

One or more embodiments of the present invention include the possibilityof creating error checking dependencies in the encoding process. Forexample, when encoding data set 522 as discussed in relation to flowdiagram 750 above, there is possibility of a data dependency occurring.Such data dependence undermines a robust code as each check is no longerindependent. The shortest path length that can be achieved without acycle is referred to as girth. The longer the girth, the less the datadependency and the more robust the code. In general, a code is definedby a minimum distance (dmin) value and a girth value. As will beappreciated by one of ordinary skill in the art upon reading thisdisclosure, dmin affects the code performance in the maximum-likelihood(ML) decoding, and the girth affects primarily belief propagation. It iswidely accepted that the belief-propagation decoding provides the bestapproximation of maximum-likelihood decoding where a given code does notexhibit cyclical dependencies.

Turning to FIG. 8 a, a lattice diagram 800 depicts a six path datadependency involving three data bits 840, 850, 860 and three checks 810,820, 830. Following lattice diagram 800, data bit 840 is check alongwith a group of other bits by a check 810 as shown by a path 801. Theresult of check 810 is used in relation to data bit 850 and other databits which are checked by check 820 as shown by paths 802, 803. Theresult of check 820 is used in relation to data bit 860 and other databits which are checked by check 820 as shown by paths 804, 805. Theresult of check 820 is fed forward to check data bit 840 as shown bypath 806. Thus, the value ascertained for data bit 840, data bit 850 anddata bit 860 is each ultimately dependent upon itself. This dependencydiminishes the ability for any code to effectively predict the value ofdata bit 840, data bit 850 and data bit 860.

The preceding dependency is illustrated in FIG. 8 b in relation to anencoded data set 822 that includes three columns of parity 824, 826,828. Three diagonal groups of bits 870, 872, 874 are defined in encodeddata set 822. The three groups share common data bits 871, 873, 875 thatare located at the intersections of the three groups. Thus, groups 870,872, 874 form a triangle with data bits 871, 873, 875 located at therespective corners of the triangles. Such a configuration results ineach of data bits 871, 873, 875 being the subject of checks (paritychecks using the parity bits in columns 824, 826, 828) common to otherof bits 871, 873, 875. This results in the dependency discussed above inrelation to lattice diagram 800. In particular, data 840 is representedby data bit 871, data 850 is represented by data bit 873, data 860 isrepresented by data bit 875, check 810 is represented by the paritycheck of group 870, check 820 is represented by the parity check ofgroup 874, and check 830 is represented by the parity check of group872.

Some embodiments of the present invention provide a code designtechnique that may be used to reduce a six path dependency (or triangledependency) such as that illustrated by FIGS. 8 a and 8 b. In somecases, a code of weight three is desired because they offer goodperformance in perpendicular recording scenarios. In such cases, analgorithm designed to avoid a triangular pattern such as that shown inFIG. 8 b may be applied. Such an approach may provide for flexibility ofdesigning both high rate and low rate codes. Such high rate codes may beof particular interest in magnetic recording.

Turning to FIG. 8 c, a flow diagram 880 depicts a method in accordancewith one or more embodiments of the present invention for avoiding theaforementioned dependencies. Following flow diagram 880, one group ofdata bits (S1) traversing a data set at an angle or slope is defined(block 881), and another group of data bits (S2) traversing the samedata set at another angle is defined (block 882). These could include,for example, groups 870, 874 of FIG. 8 b along with the other groupstraversing data set 822 at the same angle as groups 870, 874. A firstbit location (i.e., point) on the S1 group of data bits is selected(block 883) and a first bit location (i.e., point) on the S2 group ofdata bits is selected (block 884). The slope between the selected bitlocations is then determined (block 885), and the determined slope issaved in an array of slopes (block 886). This process is repeated untila slope from every one of the bits included in S1 to every bit in S2 iscalculated (blocks 887, 888, 889, 890). Once all of the slopes arecalculated, a slope for the third group of bits is defined (block 891).The slope for the third group of bits may be defined as any slope notincluded in the array of saved slopes. This will assure that atriangular pattern such as that shown in FIG. 8 b will not occur. Athird group of bits (S3) is then formed using the determined slope(block 892). This may include forming a number of groups of bits eachhaving the determined slope until all of the bits in a given array ofbits are accounted for. Once this is complete, parity such as thatdescribed above in relation to FIGS. 5 a-5 c may be calculated.

Of note, such an approach allows for the minimum distance (dmin) andgirth values for the code to be controlled. Further, based on thedisclosure provided herein, one of ordinary skill in the art willrecognize that the processes may be extended to obtain codes of girthten and girth 12 and on. Further, such an approach may be used inaccordance with one or more embodiments of the present invention todesign a simple type of LDPC codes of girth eight. Such LDPC codes canbe used in digital storage, transmission systems, and/or the like. Byencoding and reproducing information with the proposed LDPC code, it ispossible to obtain a high correcting effect, which decreases random andburst errors even at low signal to noise ratios. LDPC codes developedusing the aforementioned technique generally offer good performance,flexibility and/or reduced complexity when compared to Randomlygenerated LDPC codes which exhibit relatively high decoding/encodingcomplexity; LDPC codes created using cyclic matrix permutation that aretypically offer relatively low encoding complexity, but are typicallynot very flexible in terms of column/row weight of the parity-checkmatrix, as well as code length and rate; and LDPC codes based onrectangular integer lattices guarantee minimum distance of greater thanor equal to six and a girth of eight. However, the code rate and lengthare difficult to control.

Turning to FIG. 9, a software based system 900 in accordance with one ormore embodiments of the present invention is depicted. Software basedsystem 900 includes a processor based machine 910 and a computerreadable medium 920 that includes software or firmware (i.e.,instructions executable by a processor) to performing part of or all ofthe encoding and/or decoding functions described herein. As will beappreciate by one of ordinary skill in the art upon reading thisdisclosure, processor based machine 910 may include any type ofprocessor capable of executing software and/or firmware instructions.Thus, for example, processor based machine 910 may include amicroprocessor or a digital signal processor. Alternatively, processorbased machine 910 may simply be a microprocessor or a digital signalprocessor that is imbedded with other logic. Further, based on thedisclosure provided herein, one of ordinary skill in the art willrecognize that computer readable medium 920 may be any number of storagedevices including, but not limited to, a hard disk drive, a randomaccess memory, a non-volatile memory, and/or the like. As just someexamples, instructions maintained on computer readable medium 920 may beexecutable to perform one or more of the functions of channel detector260, decoder 280, encoder 220, channel detector 261, decoder 281,channel detector 360, decoder 380, channel detector 560, decoder 580,flow diagram 740, flow diagram 750, and/or flow diagram 880.

In conclusion, the present invention provides novel systems, devices,methods and arrangements for error reduction. While detaileddescriptions of one or more embodiments of the invention have been givenabove, various alternatives, modifications, and equivalents will beapparent to those skilled in the art without varying from the spirit ofthe invention. Therefore, the above description should not be taken aslimiting the scope of the invention, which is defined by the appendedclaims.

1. A digital information system comprising: a channel detector, whereinthe channel detector receives a data set represented as columns androws, and wherein the channel detector provides a first outputrepresenting the data set; and a decoder, wherein the decoder receivesthe first output, wherein the decoder is operable to perform three slopeparity checks, wherein the slope parity checks operate on a first groupof data bits traversing the data set at a first angle, a second group ofdata bits traversing the data set at a second angle, a third group ofdata bits traversing the data set at a third angle, and wherein thedecoder provides a second output representing the data set.
 2. Thedigital information system of claim 1, wherein the first angle isdifferent from the second angle and different from the third angle. 3.The digital information system of claim 1, wherein the slope of at leastone of the first angle, the second angle and the third angle areselected from a group consisting of: a slope greater than zero, a slopeless than zero, and a slope equal to zero.
 4. The digital informationsystem of claim 3, wherein at least one of the first angle, the secondangle and the third angle is programmable.
 5. The digital informationsystem of claim 1, wherein the data set is represented as columns androws, and wherein the slope parity checks operate on at least oneelement from each of the columns.
 6. The digital information system ofclaim 1, wherein the channel detector is selected from a groupconsisting of: a soft output Viterbi algorithm channel detector, and aMaximum A Posteriori Probability channel detector.
 7. The digitalinformation system of claim 1, wherein the decoder is a low-densityparity check decoder.
 8. The digital information system of claim 1,wherein the first angle is different from at least one of the secondangle and the third angle.
 9. The digital information system of claim 1,wherein the first angle is the same as at least one of the second angleand the third angle.
 10. A method for error reduction in a digitalinformation system, the method comprising: providing an encoded dataset, wherein the encoded data set is represented as columns and rows,and wherein the encoded data set includes: a first group of parity dataarranged as a first column of the encoded data set, a second group ofparity data arranged as a second column of the encoded data set, and athird group of parity data arranged as a third column of the encodeddata set; providing a decoding system, wherein the decoding systemincludes a channel detector and a decoder; wherein the channel detectorreceives the encoded data set and provides a channel detector outputrepresentative of the encoded data set; and wherein the decoder receivesthe channel detector output and performs a first slope parity checkusing the first group of parity data, a second slope parity check usingthe second group of parity data, and a third slope parity check usingthe third group of parity data.
 11. The method of claim 10, wherein theangle of the first slope parity check is different from the angle of thesecond slope parity check and the angle of the third parity check. 12.The method of claim 11, wherein the angle of the first slope paritycheck is programmable.
 13. The method of claim 12, wherein the angle ofthe second parity check is programmable, and wherein the angle of thethird parity check is programmable.
 14. The method of claim 10, whereinthe third group of parity data is based on data from the second group ofparity data and the first group of parity data.
 15. The method of claim14, wherein the second group of parity data is based on data from thefirst group of parity data.
 16. The method of claim 10, wherein thefirst group of parity data is exclusive of the second group of paritydata and the third group of parity data, wherein the second group ofparity data is exclusive of the first group of parity data and the thirdgroup of parity data, and wherein the third group of parity data isexclusive of the first group of parity data and the second group ofparity data.
 17. The method of claim 10, wherein the angle of the firstslope parity check is different from at least one of the angle of thesecond slope parity check and the angle of the third parity check. 18.The method of claim 10, wherein the angle of the first slope paritycheck is the same as at least one of the angle of the second slopeparity check and the angle of the third parity check.